Our favorites for planning, trip advice, guidebook suggestions, reviews and travel hacking:
Lonely Planet: for my first trip abroad in Europe, I lugged around their Western Europe on a Shoestring guidebook and never looked back. In addition to their guidebooks, they have an extensive web site of information and suggestions.
Frommers: we use this web site to get preliminary ideas on what to see and what to do for any new places are traveling to. Sometimes we might only have a day or two and just need suggestions on what to see on a limited time schedule.
TripAdvisor: we utilize the reviews on this web site to determine which hotels to avoid, and also to glean traveler tips on hotels and attractions.
The Points Guy: this web site is worth a daily visit, as it offers the latest news for loyalty promotions, credit card offers, reviews and travel secrets for people who love to save money.
Boarding Area: required reading for frequent flyers, enough said.